Searching for extrasolar biosignatures is important to understanding life on Earth and its origins. Astronomical observations of exoplanets can find such signatures, but it is difficult and impossible to claim unequivocal life detection by remote sensing of exoplanet atmospheres.

In a new study, Professor Tomonori Totani of the University of Tokyo’s Department of Astronomy proposed a different approach: Space dust may contain direct or indirect signs of life from the host world, such as fossils of microorganisms.

Professor Totani said: “I suggest we examine well-preserved grains thrown from other worlds for possible signs of life. The search for life beyond our solar system typically means searching for signs of communication, which point to intelligent life but rule out any pre-technological life. Or looking for atmospheric signatures that could indicate life, but with no direct confirmation there could always be an explanation that doesn’t require life. However, if there are signs of life in dust particles, not only can we be sure, but we can quickly detect it.

The basic hypothesis is that massive asteroid impacts could release Earth material into space. It is likely that some of the rocky material in these ejecta contains recently deceased or perhaps petrified microbes. This material comes in a wide variety of sizes and different sized bits will behave differently in space. Some of the larger fragments may fall again or enter a stable orbit around a nearby planet or star.

Space fabric
Space fabric. This piece of interplanetary dust is believed to be part of the early solar system and was found in our atmosphere, showing that light particles could survive atmospheric entry because they don’t generate much heat from friction. ©2023 NASA CC-0

In addition, some much smaller fragments could be too small to contain any discernible life. Yet grains as small as 1 micrometer (one-thousandth of a millimeter) could not only contain a single-celled organism, but could also potentially leave their host solar system and, under the right conditions, even travel to other solar systems. .

totani said, “My paper explores this idea using available data on the different aspects of this scenario. The distances and times involved can be enormous, and both reduce the likelihood that an ejecta carrying life signs from another world can even reach us. Add to that the number of phenomena in space that can destroy small objects through heat or radiation, and the chance becomes even smaller.”

“Nevertheless, I calculate that about 100,000 such grains could land on Earth each year. Given the many unknowns involved, this estimate could be too high or too low, but the means to investigate it already exist, so it’s worth pursuing.

“Perhaps there are already such grains on Earth and in abundant quantities. Space dust could be recovered relatively easily, but distinguishing extrasolar material from material originating in our solar system is still a complex matter. Yet there are existing missions that use ultra-lightweight substances known as aerogels to trap dust in the vacuum cleaner in space.”

totani said, “I hope that researchers in various fields are interested in this idea and will explore the feasibility of this new search for extrasolar life in more detail.”

Magazine reference:

  1. Tomonori Totani. “Solid grains ejected from terrestrial exoplanets as a probe of the galactic abundance of life,” International Journal of Astrobiology. DOI: 10.48550/arXiv.2210.07084